spam: A Sparse Matrix R Package with Emphasis on MCMC Methods for Gaussian Markov Random Fields

spam is an R package for sparse matrix algebra with emphasis on a Cholesky factorization of sparse positive definite matrices. The implemantation of spam is based on the competing philosophical maxims to be competitively fast compared to existing tools and to be easy to use, modify and extend. The first is addressed by using fast Fortran routines and the second by assuring S3 and S4 compatibility. One of the features of spam is to exploit the algorithmic steps of the Cholesky factorization and hence to perform only a fraction of the workload when factorizing matrices with the same sparsity structure. Simulations show that exploiting this break-down of the factorization results in a speed-up of about a factor 5 and memory savings of about a factor 10 for large matrices and slightly smaller factors for huge matrices. The article is motivated with Markov chain Monte Carlo methods for Gaussian Markov random fields, but many other statistical applications are mentioned that profit from an efficient Cholesky factorization as well.

A spatial analysis of multivariate output from regional climate models

Climate models have become an important tool in the study of climate and climate change, and ensemble experiments consisting of multiple climate-model runs are used in studying and quantifying the uncertainty in climate-model output. However, there are often only a limited number of model runs available for a particular experiment, and one of the statistical challenges is to characterize the distribution of the model output. To that end, we have developed a multivariate hierarchical approach, at the heart of which is a new representation of a multivariate Markov random field. This approach allows for flexible modeling of the multivariate spatial dependencies, including the cross-dependencies between variables. We demonstrate this statistical model on an ensemble arising from a regional-climate-model experiment over the western United States, and we focus on the projected change in seasonal temperature and precipitation over the next 50 years.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS369 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Extremal Quantum Correlations and Cryptographic Security

We investigate a fundamental property of device independent security in quantum cryptography by characterizing probability distributions which are necessarily independent of the measurement results of any eavesdropper. We show that probability distributions that are secure in this sense are exactly the extremal quantum probability distributions. This allows us to give a characterization of security in algebraic terms. We apply the method to common examples for two-party as well as multi-party setups and present a scheme for verifying security of probability distributions with two parties, two measurement settings, and two outcomes.Comment: 7 pages, 2 figures, revised version, accepted for publication in Phys. Rev. Let

spam: A Sparse Matrix R Package with Emphasis on MCMC Methods for Gaussian Markov Random Fields

spam is an R package for sparse matrix algebra with emphasis on a Cholesky factorization of sparse positive definite matrices. The implemantation of spam is based on the competing philosophical maxims to be competitively fast compared to existing tools and to be easy to use, modify and extend. The first is addressed by using fast Fortran routines and the second by assuring S3 and S4 compatibility. One of the features of spam is to exploit the algorithmic steps of the Cholesky factorization and hence to perform only a fraction of the workload when factorizing matrices with the same sparsity structure. Simulations show that exploiting this break-down of the factorization results in a speed-up of about a factor 5 and memory savings of about a factor 10 for large matrices and slightly smaller factors for huge matrices. The article is motivated with Markov chain Monte Carlo methods for Gaussian Markov random fields, but many other statistical applications are mentioned that profit from an efficient Cholesky factorization as well

Sharing the spirit? Sociospatial polarization and expressed enthusiasm for the Olympic Games

This article seeks to contribute to the literature that assesses the local outcomes of hosting hallmark events by examining the expressed levels of enthusiasm for the year 2000 Olympic Games within Sydney. We report on the results of a telephone survey of 658 Sydney residents conducted in February 1998 designed to measure enthusiasm for the 2000 Olympic Games. As of February 1998, it appeared that enthusiasm for the 2000 Olympics remained strong in Sydney, thereby providing support to the views of those who regard hallmark events as a psychological mechanism to assist residents to feel a sense of pride in their city and nation. However, higher levels of enthusiasm were recorded in the lower socioeconomic status suburbs of Western Sydney than in the higher status suburbs of the North Shore. These differences were not statistically differentiated by economic indicators (income, occupation, and education levels) but were significant by association with social variables such as country of birth, age, and marital and family status. Several implications of these results are considered within the literature debating the outcome of hosting hallmark events

Pericardial biopsy and fenestration

Employing a video thoracoscopic pericardial fenestration constitutes a promising technique for the investigation and treatment of chronic pericardial effusions. It combines the benefit of low invasiveness with the advantages of open biopsy. The procedure simultaneously allows both an accurate diagnosis under visual control (inspection, aspiration, well targeted biopsy of pathological processes) and the performance of effective therapeutic intervention. Without imposing unacceptable stress, it also facilitates rapid symptom relief in patients with advanced malignant disease whose general condition is severely impaire